Multi-channel SMPS is widely used in SSD power systems for it can provide multiple independent output voltages. Multi-channel SMPS comprises a plurality of switching circuits, and each of the plurality of switching circuit may comprise a switch, hereinafter multi-channel SMPS is abbreviated as SMPS. On one hand, when the plurality of switching circuits are in heavy load, and the switches of the plurality of switching circuits are turned on simultaneously, thus each of the plurality of switching circuits draws a current from an input capacitor of the SMPS simultaneously. Accordingly a huge input capacitor is required for the SMPS to ensure that the input voltage of the input capacitor will not drop abruptly. So the switches of the plurality of switching circuits are required to turn on in sequence and the phase differences between each two adjacent switching circuits are required to be the same to decrease the requirement of the input capacitor. On the other hand, when one or more switching circuits are in light load, the switching frequency of the relevant switching circuit is decreased to reduce the output energy of this switching circuit. Further when one switching circuit skips from light load to heavy load, the relevant switch is required to turn on in sequence and the phase differences between each two adjacent switching circuits are required to be the same.
A control method for traditional SMPS is generating a fast system clock at first, and then generating N clock control signals based on the fast system clock to control the relevant switches of the plurality of switching circuits. The drawback of this method is that no matter one switching circuit is in light load or heavy load, the relevant clock control signal is formed at the trigger of the preset pulses of the fast system clock corresponding to the relevant clock control signal, so the output voltage ripple of this switching circuit is big when it is in light load.
So a better method is required to decrease the output voltage ripple when the switching circuit is in light load.